come across vs get on to

come across

verb
  • Used other than figuratively or idiomatically: see come, across. 

  • To find, usually by accident. 

  • To produce what was desired; come up with the goods. 

  • To give an appearance or impression; to project a certain image. 

  • To change sides; to cross over to work for the opposition. 

get on to

verb
  • Used other than figuratively or idiomatically: see get on, to. 

  • To contact (someone) in order to raise or discuss a certain matter. 

  • To progress to; to start working on. 

How often have the words come across and get on to occurred in a corpus of books? (source: Google Ngram Viewer )